[MPI3 Fortran] Results of San Jose Forum meeting

[Bill Long]

Rolf Rabenseifner wrote:
> Hi all,
> 
> I expect, that in our special case, the alignment problems cannot
> cause problems, because all is Fortran INTEGER and therefore
> at least 4-byte-aligned.
> With intentionally misaligned handles, the new derived type handle
> seems to work better (but not worse) than integer handles.
> 
> I've attached a small test code to solve the question, whether 
>  - INTEGER and
>  - TYPE handle; SEQUENCE INTEGER :: val; END TYPE handle
> is passed to a C back-end in the same way.
> 
> Does it produce the expected results on all compilers:
> 
>     IBM (several compilers)
>     Cray (ditto?)

We let you get by with this code (to the extent that 24 is OK for 
"expected 25").  However....


>     NAG Fortran
>     Intel
>     gfortran
>     Oracle/Sun
>     Pathscale
>     Portland Group
>     Possibly g95
> 
> I checked with Intel:
> 
>   cc -c handle_test_c.c
>   ifort -o handle_test handle_test.f90 handle_test_c.o
> 
>   fortcom: Warning: handle_test.f90, line 42: The structure contains one or more misaligned fields.   [SEQUENCE_A]
>     TYPE sequence_A
>   -------^
>   fortcom: Warning: handle_test.f90, line 49: The structure contains one or more misaligned fields.   [SEQUENCE_B]
>     TYPE sequence_B
>   -------^


These objections are allowable.

Have you tried the same program with all of the sequence types replaced 
with bind(c) types?   I'm guessing that the messages will go away if you 
make that change. And you get the desired output.

Cheers,
Bill


> 
>   ./handle_test
> 
>   hd_1 = 12, hd_2 = 13  (expected: 12, 13)
>   hd_i=112, hd_t%val=113 (expected: 112, 113)
>  
>   hd_1 = 14, hd_2 = 15  (expected: 14, 15)
>   strA%handle=114, strB%handle%val=115 (expected: 114, 115)
>  
>   hd_1 = 24, hd_2 = 75  (expected: 25, 75)
>   strA%handle=225, seqB%handle%val=775 (expected: 225, 775)
>  
>   handle_test(12868): unaligned access to 0x600000000000cf29, ip=0x4000000000003530
>   hd_1 = 84, hd_2 = 35  (expected: 84, 35)
>   handle_test(12868): unaligned access to 0x600000000000cf29, ip=0x4000000000003571
>   seqA%handle=884, strB%handle%val=335 (expected: 884, 335)
>  
>   handle_test(12868): unaligned access to 0x600000000000cf29, ip=0x4000000000003530
>   hd_1 = 94, hd_2 = 95  (expected: 94, 95)
>   handle_test(12868): unaligned access to 0x600000000000cf29, ip=0x4000000000003571
>   seqA%handle=994, seqB%handle%val=995 (expected: 994, 995)
> 
> Result:
> All works, but there is really a small difference:
>  - With misaligned INTEGER handle seqA, some runtime warnings occur
>  - With new derive-type handle seqB, **NO** runtime warnings occur
> 
> It would be helpful, if you can check with some other compilers.
> 
> If you find another alignment problem with some other tests for
> exactly these two types (no other derived types),
> then please can you report.
> 
> The test program should test, whether internally the Fortran
> compiler produces a subroutine call with an argument list
> for both handle types that fits to the same C back-end: int*.
> 
> Rolf
> 
> ----- "N.M. Maclaren" <nmm1 at cam.ac.uk> wrote:
> 
>> Sorry.  Posted in haste, and I forgot a critical paragraph.
>>
>> With those structures, also try seeing what they do when you remove
>> each of 'x' and 'y' in turn.  Specifically, does 'z' continue to be
>> in the same location?
>>
>> In the SPECIFIC example of a single default integer in a sequence
>> type, it will a rare compiler that lays it out differently.  But
>> all of the INTEGER, INTEGER BIND(C), sequence type and derived type
>> without the SEQUENCE may have different sizes and alignments.  And,
>> on SOME systems, a pointer to one of those may not be usable as a
>> pointer to another.
>>
>>
>>
>> _______________________________________________
>> mpi3-fortran mailing list
>> mpi3-fortran at lists.mpi-forum.org
>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-fortran
> 

-- 
Bill Long                                           longb at cray.com
Fortran Technical Support    &                 voice: 651-605-9024
Bioinformatics Software Development            fax:   651-605-9142
Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101